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CS 5565 Network Architecture and Protocols Lecture 25 Announcements

This lecture covers the announcements for CS 5565 Network Architecture and Protocols, including project deadlines, extra credit opportunities, and additional required readings.

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CS 5565 Network Architecture and Protocols Lecture 25 Announcements

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  1. CS 5565Network Architecture and Protocols Godmar Back Lecture 25

  2. Announcements • Project 2B due in 2 parts: • Apr 29 and May 6 • See bugfix to sloop topology • Please observe posted timeouts! • Extra Credit Opportunities: • Expand simulator (and your implementation) to introduce multiple link failures and link resurrection • Additional, requiring reading posted • Andersen et al [SIGCOMM’08]: Accountable Internet Protocol (AIP) • Casado et al [HotNets’08]: Rethinking Packet Forwarding Hardware CS 5565 Spring 2009

  3. Ethernet

  4. Switches vs Routers mail server to external network web server router switch IP subnet switch switch hub switch CS 5565 Spring 2009

  5. Switches vs. Routers • both store-and-forward devices • routers: network layer devices (examine network layer headers) • switches are link layer devices • routers maintain routing tables, implement routing algorithms • switches maintain switch tables, implement filtering, learning algorithms + spanning tree algorithms CS 5565 Spring 2009

  6. Hubs vs. Routers vs. Switches CS 5565 Spring 2009

  7. PPP CS 5565 Spring 2009

  8. Point to Point Data Link Control • one sender, one receiver, one link: easier than broadcast link: • no Media Access Control • no need for explicit MAC addressing • e.g., dialup link, ISDN line • popular point-to-point DLC protocols: • PPP (point-to-point protocol) • HDLC: High level data link control (Data link used to be considered “high layer” in protocol stack!) CS 5565 Spring 2009

  9. PPP Design Requirements [RFC 1547] • simplicity: reflected in non-requirements • packet framing: encapsulation of network-layer datagram in data link frame • carry network layer data of any network layer protocol (not just IP) at same time • ability to demultiplex upwards • bit transparency: must carry any bit pattern in the data field • error detection (no correction) • connection liveness: detect, signal link failure to network layer • network layer address negotiation: endpoint can learn/configure each other’s network address CS 5565 Spring 2009

  10. PPP non-requirements • no error correction/recovery • no flow control • out of order delivery OK • no need to support multipoint links (e.g., polling) Error recovery, flow control, data re-ordering all relegated to higher layers! CS 5565 Spring 2009

  11. PPP Data Frame • Flag: delimiter (framing) • Address: does nothing (only one option) • Control: does nothing; in the future possible multiple control fields • Protocol: upper layer protocol to which frame delivered (eg, PPP-LCP, IP, IPCP, etc) • Info: upper layer data being carried • Check: cyclic redundancy check for error detection CS 5565 Spring 2009

  12. Byte Stuffing flag byte pattern in data to send flag byte pattern plus stuffed byte in transmitted data CS 5565 Spring 2009

  13. PPP Data Control Protocol • Before exchanging network-layer data, data link peers must • configure PPP link (max. frame length, authentication) (see next slide) • learn/configure network layer information • for IP: carry IP Control Protocol (IPCP) msgs (protocol field: 8021) to configure/learn IP address CS 5565 Spring 2009

  14. PPP Link Control Protocol States CS 5565 Spring 2009

  15. ATM & MPLS CS 5565 Spring 2009

  16. ATM and MPLS • ATM, MPLS separate networks in their own right • different service models, addressing, routing from Internet • of technical interest in their own right • Viewed by Internet as logical link connecting IP routers • just like dialup link is really part of separate network (telephone network) CS 5565 Spring 2009

  17. Asynchronous Transfer Mode: ATM • 1990’s/00 standard for high-speed (155Mbps to 622 Mbps and higher) Broadband Integrated Service Digital Network architecture • Goal:integrated, end-end transport of carry voice, video, data • meeting timing/QoS requirements of voice, video (versus Internet best-effort model) • “next generation” telephony: technical roots in telephone world • packet-switching (fixed length packets, called “cells”) using virtual circuits CS 5565 Spring 2009

  18. ATM Architecture • adaptation layer: only at edge of ATM network • data segmentation/reassembly • roughly analogous to Internet transport layer • ATM layer: “network” layer • cell switching, routing • physical layer CS 5565 Spring 2009

  19. ATM Adaptation Layer (AAL) • ATM Adaptation Layer (AAL): “adapts” upper layers (IP or native ATM applications) to ATM layer below • AAL present only in end systems, not in switches • AAL layer segment (header/trailer fields, data) fragmented across multiple ATM cells • analogy: TCP segment in many IP packets CS 5565 Spring 2009

  20. ATM Adaptation Layer (AAL) [more] Different versions of AAL layers, depending on ATM service class: • AAL1: for CBR (Constant Bit Rate) services, e.g. circuit emulation • AAL2: for VBR (Variable Bit Rate) services, e.g., MPEG video • AAL5: for data (e.g., IP datagrams) User data AAL PDU ATM cell CS 5565 Spring 2009

  21. ATM Layer: Virtual Circuits • VC transport: cells carried on VC from source to dest • call setup, teardown for each call before data can flow • each packet carries VC identifier (not destination ID) • every switch on source-dest path maintain “state” for each passing connection • link,switch resources (bandwidth, buffers) may be allocated to VC: to get circuit-like performance • Permanent VCs (PVCs) • long lasting connections • typically: “permanent” route between to IP routers • Switched VCs (SVCs): • dynamically set up on per-call basis CS 5565 Spring 2009

  22. ATM VCs • Advantages of ATM VC approach: • QoS performance guarantee for connection mapped to VC (bandwidth, delay, delay jitter) • Drawbacks of ATM VC approach: • Inefficient support of datagram traffic • “cell-tax” • one PVC between each source/dest pair does not scale (N^2 connections needed) • SVC introduces call setup latency, processing overhead for short lived connections CS 5565 Spring 2009

  23. ATM Layer: ATM cell • 5-byte ATM cell header • 48-byte payload • small payload -> short cell-creation delay for digitized voice • halfway between 32 and 64 (compromise!) Cell header Cell format CS 5565 Spring 2009

  24. ATM Cell Header • VCI: virtual channel ID • will change from link to link thru net • PT:Payload type (e.g. RM cell versus data cell) • CLP: Cell Loss Priority bit • CLP = 1 implies low priority cell, can be discarded if congestion • HEC: Header Error Checksum • cyclic redundancy check CS 5565 Spring 2009

  25. ATM Physical Layer (more) • Two pieces (sublayers) of physical layer: • Transmission Convergence Sublayer (TCS): • adapts ATM layer above to PMD sublayer below • TCS Functions: • Header Checksum generation: 8 bits CRC • Cell delineation • Physical Medium Dependent (PMD) CS 5565 Spring 2009

  26. ATM Physical Layer Physical Medium Dependent (PMD) Sublayer Examples: • SONET/SDH: transmission frame structure (like a container carrying bits) • bit synchronization • bandwidth partitions (TDM) • several speeds • T1/T3: transmission frame structure (old telephone hierarchy): 1.5 Mbps/45 Mbps CS 5565 Spring 2009

  27. SONET/SDH Speeds CS 5565 Spring 2009

  28. ATM: where does it fit in? Vision: end-to-end transport: “ATM from desktop to desktop” • ATM is a network technology Reality: used to connect IP backbone routers • “IP over ATM” • ATM as switched link layer, connecting IP routers • NB: ATM can also connect other networks IP network ATM network CS 5565 Spring 2009

  29. ATM network Ethernet LANs IP-Over-ATM • IP over ATM • replace “network” (e.g., LAN segment) with ATM network • ATM addresses, IP addresses • ARP for ATM Classic IP only • 3 “networks” (e.g., LAN segments) • MAC (802.3) and IP addresses Ethernet LANs CS 5565 Spring 2009

  30. app transport IP AAL ATM phy app transport IP Eth phy ATM phy ATM phy IP AAL ATM phy Eth phy IP-Over-ATM (2) CS 5565 Spring 2009

  31. PPP or Ethernet header IP header remainder of link-layer frame MPLS header label Exp TTL S 5 1 3 20 Multi-Protocol Label Switching (MPLS) • initial goal: speed up IP forwarding by using fixed length label (instead of IP address) to do forwarding • borrowing ideas from Virtual Circuit (VC) approach • but IP datagram still keeps IP address! • today’s use: • traffic engineering • VPNs (Virtual Private Networks) CS 5565 Spring 2009

  32. MPLS Capable Routers • a.k.a. label-switched router • groups packets in FEC (forwarding equivalence classes), assign labels to FECs • forwards packets to outgoing interface based only on label value (don’t inspect IP address) • MPLS forwarding table distinct from IP forwarding tables • signaling protocol needed to set up forwarding • RSVP-TE • forwarding possible along paths that IP alone would not allow (e.g., source-specific routing) • can be stacked, multiple MPLS labels • must co-exist with IP-only routers (at edges) CS 5565 Spring 2009

  33. in out out label label dest interface 10 6 A 1 12 9 D 0 in out out label label dest interface in out out label label dest interface 8 6 A 0 6 - A 0 MPLS forwarding tables in out out label label dest interface 10 A 0 12 D 0 8 A 1 R6 0 0 D 1 1 R3 R4 R5 0 0 A R2 R1 CS 5565 Spring 2009

  34. A brief look back to history CS 5565 Spring 2009

  35. The Internet: Virtualizing Networks • … differing in: • addressing conventions • packet formats • error recovery • routing 1974: multiple unconnected nets • ARPAnet • data-over-cable networks • packet satellite network (Aloha) • packet radio network "A Protocol for Packet Network Intercommunication", V. Cerf, R. Kahn, IEEE Transactions on Communications, May, 1974, pp. 637-648. satellite net ARPAnet CS 5565 Spring 2009

  36. Cerf & Kahn’s Vision:An Internetwork Architecture • What is virtualized? • two layers of addressing: internetwork and local network • new layer (IP) makes everything homogeneous at internetwork layer • underlying local network technology • cable • satellite • 56K telephone modem • today: ATM, MPLS • … “invisible” at internetwork layer. • Looks like a link layer technology to IP! CS 5565 Spring 2009

  37. Internetwork layer (IP): • addressing: internetwork appears as a single, uniform entity, despite underlying local network heterogeneity • network of networks The Internet: Virtualizing Networks Gateway: • “embed internetwork packets in local packet format or extract them” • route (at internetwork level) to next gateway gateway satellite net ARPAnet CS 5565 Spring 2009

  38. principles behind data link layer services: error detection, correction sharing a broadcast channel: multiple access link layer addressing instantiation and implementation of various link layer technologies Ethernet, switched LANS, Interconnecting LANs Point-to-Point Protocols: HDLC, PPP virtualized networks as a link layer: ATM, MPLS Summary CS 5565 Spring 2009

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